Chinese scientists’ claims for new quantum code-breaking algorithm raise eyebrows in the US
- Today’s mainstream encryption may be vulnerable within years instead of decades after Chinese researchers propose new code-breaking algorithm
- ‘There’s the nagging question of why the Chinese government didn’t classify this research,’ US cryptographer writes
But some senior security and quantum experts in the United States have raised concerns as well as doubts about that claim coming out of China.
Quantum computers can speed up the factoring of large numbers – a difficult task for traditional computers – to break codes in a relatively short period.
But it is commonly believed that such a machine would need to handle millions of qubits, the basic unit of quantum information, to hack a bank account protected by state-of-the-art encryption.
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Osprey, the most powerful quantum computer in the world launched by IBM in November, operates with 433 qubits and is nowhere near breaking codes.
The Chinese team, led by Professor Long Guilu of Tsinghua University, said its new algorithm could dramatically reduce the scale of a practical quantum computer to 372 qubits – even less than that of Osprey.
The quantum code-breaking machine can decipher data encrypted with RSA-2048, one of the highest industrial standards adopted by many governments, financial institutions and tech companies to protect information security using a 2048-bit-long key, according to the Chinese researchers.
Based on a controversial algorithm developed by German mathematician Claus Schnorr in 2013, the Chinese team developed a new algorithm called sublinear-resource quantum integer factorisation (SQIF) to optimise the quantum calculation process.
To demonstrate the feasibility of SQIF, the researchers broke a 48-bit-length encryption key with a tiny 10-qubit superconductive quantum computer at Zhejiang University in Hangzhou.
It is “the most qubit-saving factorisation algorithm to date,” they said in the paper.
Because quantum computers handling hundreds of qubits could be developed in the near future, “our study shows great promise in expediting the application of current noisy quantum computers, and paves the way to factor large integers of realistic cryptographic significance,” they added.
Bruce Schneier, an American cryptographer and computer expert who has testified in the US Congress on information security issues, said the Chinese study “is something to take seriously”.
“It might not be correct, but it’s not obviously wrong,” Schneier, the chief of security architecture at Inrupt, said in a post on his blog on January 3.
“And there’s the nagging question of why the Chinese government didn’t classify this research,” he added.
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Scott Aaronson, director of the quantum information centre at the University of Texas at Austin, acknowledged Schneier’s concern but said he did not believe Long’s method would work.
He said a major problem with the paper was its failure to clarify the advantage of quantum technology over classical computers.
“It seems to me that a miracle would be required for the approach here to yield any benefit at all, compared to just running the classical Schnorr’s algorithm on your laptop,” Scott wrote on his blog.
“This is one of the most actively misleading quantum computing papers I’ve seen in 25 years, and I’ve seen many,” he added.
Peter Shor, the professor of applied mathematics at MIT who invented the Shor’s algorithm, posted on Twitter: “There are apparently possible problems with this paper”. He was replying to a post by a scientist in Google’s quantum programme called Craig Gidney, who alleged the Chinese team omitted crucial technical details to back up their claim.
“If it is true it is catastrophic,” said Lawrence Gasman, founder and president of Inside Quantum Technology, a website on developments in quantum technology.
“But as one of my old professors at MBA school said, ‘If an idea is interesting it is probably wrong’,” Gasman said. “We should also consider that this emanates from China, a place desperate to prove that it is better than the US.”
Long’s collaborators included researchers from the State Key Laboratory of Mathematical Engineering and Advanced Computing, a military-affiliated research institute in Zhengzhou, Henan province. It was established jointly by the PLA’s Information Engineering University and Wuxi Jiangnan Institute of Computing Technology.
The team could not be reached for comment.
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A Beijing-based cryptographer who knew Long personally said he did not believe the paper was thrown out as a smoke screen to mislead the US and other competing countries with intentional false claims.
“Professor Long conducts solid research and keeps a low profile. He will not put his academic reputation at stake for the game of geopolitics,” said the researcher who asked not to be named because of the sensitivity of the issue.
The Beijing source said it was too early to reach a verdict on the paper until it went through rigorous peer review.
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Sharing the academic findings with the international community would not undermine China’s national security as long as the paper did not contain engineering details on how to scale up the code-breaking capability to practical levels, according to the researcher.
“The chance that the existing encryption technology is under immediate threat is small. Even if it really happens, it will not be the end of the world,” the researcher said.
“Many countries, including China and the US, have developed new industrial encryption standards that can stand against quantum-code breaking. They can replace existing methods quickly if a threat is confirmed,” he added.
